I changed out the fluid on my front and rear differentials and transfer case this weekend, as it has been 25k miles since it was last done by the previous owner. I also have heard a faint scraping/whirring sound at low speed since I bought it. I'm now at 100k miles.

Front diff and transfer case oils came out looking nearly brand new. Clear and light colored (for those doing the transfer case, be forewarned, it can take far more than the 1.5L listed capacity, I put in 1.8L before I realized).

Rear differential was a different story. The oil was nearly black and swirled with metal particles. The magnet on the drain plug had picked up a heavy coating of these metal particles. Nothing like big chunks, just very fine glitter.

So what should I do about the rear differential? Should I change the oil again in another 5k or 10k miles to help flush it? Just leave it and pray? Trade it in for an LR4?

 

I'm not sure why this is even a question. You should change it again in 5k and see what it looks like. If the sound you are hearing is indeed the diff, then you will know soon enough and at that point you can change it; no harm no foul.

 

Well I guess what I was trying to get at (from anyone with experience) is how long till I need a new diff? Can I hope to keep the diff alive for another 30-50k miles with regular changes or should I just not bother and save the $$ for a new/used diff?

 

I guess I don't think it's that much money...it's probably $200 to get the diff oil changed versus $4000 to get a new diff; so I think the risk/reward works out in favor of changing the oil at least one more time to see if it helps or if the noise doesn't progress. It would also be worthwhile to go get it looked at (or listened to) with chassis ears to see if the whirring sound you hear is even the diff and not a wheel bearing or something else.

I feel your pain on the diffs though...mine are not original, and on this set I am totally babying them in terms of oil. I was changing the oil every couple thousand (like a break-in procedure) until they both came back clean as a whistle. Now I'll go to every 15,000 Miles.

 

Or you can just buy the GM fluid for $30/liter and do two oil changes for $90. I can't help you with planning for a new diff unfortunately. No idea how long yours might last.

 

You could do that...but for me, I only fill my diff with 100% genuine OEM Unicorn ****.

 

Lol! I always imagined unicorn **** would smell better!

 

Fair point....that stuff is STINKY!

 

Actually, it looked pretty similar to the fluid and the build up on the magnet in this video which makes me think it's fairly normal:


Maybe I'm OK then? Just shocked me how different front and rear were.

 

Bah you're fine. I used to fret about this. Change with decent oil (redline has gotten good, or dealer stuff), and check level/quality every once in a while.

If you start hearing terrible noises, use an IR heat gun on the diff. Higher than 180F start finding a new one. Had a bad one that did 30k and would get to maybe 160F on a warm day.